Structural versatility of peptides from Cα,α-disubstituted glycines: crystal-state conformational analysis of peptides from Cα-methylhomophenylalanine, (αMe)Hph

The molecular and crystal structures of the C^α-tetrasubstituted, δ-branched α-amino acid C^α-methyl-homophenylalanine, H-d -(αMe)Hph-OH, and three peptides (to the pentamer level), including the homotripeptide, have been determined by X-ray diffraction. The peptides are Z-l -(αMe)Hph-(l -Ala)₂-OMe, pBrBz-[d -(αMe)Hph]₃-OtBu and Ac-(Aib)₂-l -(αMe)Hph-(Aib)₂-OtBu. All the (αMe)Hph residues prefer φ,ψ torsion angles in the helical region of the conformational map. The two terminally blocked tripeptides adopt a β-bend conformation stabilized by a 1→4 C = O?H-N intramolecular H-bond. The terminally blocked pentapeptide is folded in a regular 3₁₀-helix. In general, the relationship between (αMe)Hph α-carbon chirality and helix handedness is the same as that exhibited by protein amino acids. A comparison is also made with the conclusions extracted from published work on peptides from other types of C^α-alkylated aromatic α-amino acids. © Munksgaard 1996.     

Assessment of RNA amplification by multiplex RT‐PCR and IgM detection by indirect and capture ELISAs for the diagnosis of measles and rubella

Sanz JC, Mosquera M, Ramos B, Ramírez R, de Ory F, Echevarria JE. Assessment of RNA amplification by multiplex RT‐PCR and IgM detection by indirect and capture ELISAs for the diagnosis of measles and rubella. APMIS 2010; 118: 203–9. The aim of the study was to compare RNA amplification using multiplex RT‐PCR and IgM detection by means of indirect and capture ELISAs for the diagnosis of measles and rubella. A total of 229 cases of maculopapular rash with serum and throat swab samples were included. Specific serological IgM to measles and rubella was determined by Enzygnost^® (Siemens) and Platelia^TM (Bio‐Rad). Both viruses were researched using multiplex RT‐PCR performed on throat samples. Criteria for inclusion of measles or rubella cases were a positive RT‐PCR result for one virus and negative for the other; and/or a positive IgM result for one virus by both ELISAs and negative RT‐PCR for the other virus. A total of 74 cases were classified as measles and 54 as rubella. In measles, sensitivity and specificity were 93.2% and 100% for RT‐PCR, 97.3% and 98.1% for Enzygnost^®, and 90.5% and 95.5% for Platelia^TM. For rubella, these values were 42.6% and 100% for RT‐PCR, 100% and 97.1% for Enzygnost^®, and 94.4% and 98.3% for Platelia^TM. Enzygnost^® and Platelia^TM are useful techniques for detecting IgM against measles and rubella. RNA amplification by RT‐PCR was both sensitive and specific for the diagnosis of measles; however, for rubella, the sensitivity of this technique must be improved.     

Wolff-Parkinson-White Syndrome Presenting as the Permanent Form of Junctional Reciprocating Tachycardia

Permanent Reciprocating Tachycardia and Preexcitation. The substrate of the permanent form of junctional reciprocating tachycardia is an accessory pathway with no spontaneous anterograde conduction, usually located in the posteroseptal area. We report a case of this type of tachycardia with overt anterograde ventricular preexcitation. Electrophysiologic study confirmed that tachycardia was due to an accessory pathway with long retrograde conduction time; electrophysiologic findings suggested longitudinal dissociation of the accessory pathway. Radiofrequency application at the coronary sinus os resulted in disappearance of preexcitation and cure of the tachycardia.     

Quantitative ultrasound of bone and calcium intake in suburban males in Sri Lanka

Background: While only 30% of all hip fractures occurred in Asia in 1990, more than 50% will occur by the year 2050. We investigated the relationship between the Stiffness Index (SI), assessed with quantitative ultrasound, and calcium intake in a cross‐sectional survey of suburban males of different ages. Methods: From 496 people who were invited, 274 participated (55%). A single operator performed quantitative ultrasound measurements at the right calcaneus using Lunar Achilles. We derived the Sri Lankan T‐score values for SI. Calcium intake was measured using semiquantitative food frequency questionnaire to measure the previous 7 days intake. Results: There was gradual decrease in mean SI from the age of 30 years. Eighty percent of the men between 21–40 years had normal T‐scores. This percentage value fell to high 60s in men between 41–70 years. After 71 years, 35% had normal T‐scores and 30% had T‐scores less than –2.5. The mean calcium intake was 197 mg/day (95% CI 187–287 mg). Conclusions: This is the first population‐based study done in Sri Lanka regarding calcium intake and SI in males. Although few men had low T‐scores according to SI after 40 years, bone health of elderly (after 71 years) is at risk levels. The overall prevalence of low SI was negligible (4%) even with low calcium intake. Age is the only factor that influenced SI.     

Structural characterizations of neuropeptide tyrosine (NPY) and its agonist analog [Ahx5-17]NPY by NMR and molecular modeling

The structures of human NPY and of its centrally truncated agonist analog [Ahx^5–17]NPY have been investigated in DMSO-d₆ by two-dimensional NMR and by molecular modeling. For both peptides, a complete resonance assignment was achieved and a large number (more than 200) of inter-residue NOE connectivities were observed, including long-range connectivities between the N- and C-terminal ends of the chain. Molecular models were calculated using NOE constraints by distance geometry, simulated annealing and conjugate gradient energy minimization. The results indicate that both peptides are folded in the center of their chain, NPY adopting the hairpin shape, whereas the central portion of [Ahx^5–17]NPY is characterized by relatively large loops. In contrast to previous models, practically no α-helical structure exists for these peptides under our conditions, but two β-turns are found in NPY and one in [Ahx^5–17]NPY. The proximity of the terminal ends could be the determinant factor for their activity. © Munksgaard 1995.